selftests: net: py: avoid masking exceptions in bkg() failures

bkg() failures are currently quite hard to debug and spot.
Often we have code along the lines of:

  with bkg("./cmd_rx_something -p PORT"):
       wait_port_listen(PORT)
       cmd("./cmd_tx_something", host=remote)

When wait_port_listen() fails we don't get to see the exit status
of bkg(). Even tho very often it's a failure in the bkg() command
that's actually to blame. Try not to interfere with the bkg()
command error checking.

With:

   with bkg("false", exit_wait=True):
        time.sleep(0.01)  # let the 'false' cmd run
        raise Exception("bla")

Before:

  .. stack trace ..
  # Exception| Exception: bla

After:

  .. stack trace ..
  # Exception| Exception: bla
  # Exception|
  # Exception| During handling of the above exception, another exception occurred:
  .. stack trace ..
  # Exception| lib.py.utils.CmdExitFailure: Command failed: false
  # Exception| STDOUT: b''
  # Exception| STDERR: b''

Reviewed-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260223202633.4126087-2-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/tools/testing/selftests/net/lib/py/utils.py b/tools/testing/selftests/net/lib/py/utils.py
index 85884f3e827b69dfe7cc15a4fddc0f61f1331900..8fa1c2fabfc28a9847b6b62c71a3aba32cb00315 100644 (file)
--- a/tools/testing/selftests/net/lib/py/utils.py
+++ b/tools/testing/selftests/net/lib/py/utils.py
@@ -159,8 +159,11 @@ class bkg(cmd):
         return self
 
     def __exit__(self, ex_type, ex_value, ex_tb):
-        # Force termination on exception
-        terminate = self.terminate or (self._exit_wait and ex_type is not None)
+        terminate = self.terminate
+        # Force termination on exception, but only if bkg() didn't already exit
+        # since forcing termination silences failures with fail=None
+        if self.proc.poll() is None:
+            terminate = terminate or (self._exit_wait and ex_type is not None)
         return self.process(terminate=terminate, fail=self.check_fail)